1. Field of the Invention
The present invention relates to a melt-moldable, thermoplastic norbornene-based resin composition, and molded article or optical film using the same, more particularly a thermoplastic norbornene-based resin composition having improved moldability, moisture permeability and adhesiveness, among others, and controlled in thermal degradation and defect formation during the melt molding process while retaining the inherent advantages of norbornene-based resin, e.g., heat resistance and transparency, and article or optical film produced by melt-molding the same composition.
2. Description of the Prior Art
Thermoplastic norbornene-based resin composition has been widely used in various areas, centered by optical areas, e.g., lenses (e.g., those for common cameras, video cameras, telescopes, glasses and laser beams), optical disks (e.g., optical video, audio, document filing and memory disks), optical materials (e.g., those for optical fibers), and other optical uses (e.g., image-transferring sheets, various films and other sheets); and other areas, e.g., cases for various electronic devices, window glasses, printed boards, sealants and inorganic or organic binders, in which its excellent properties, e.g., transparency, heat resistance, low moisture absorptivity, low birefringence and moldability, are utilized.
For these optical areas, in particular for optical films, e.g., phase-difference films and polarizing plate protective films, thermoplastic norbornene-based polymer is a suitable resin material. For example, Japanese Patent Laid-open Publication Nos.62-181365 and 6-51117 describe these optical films, discussing that thermoplastic norbornene-based polymer is suitable for the optical films because of its excellent properties, e.g., transparency, heat resistance, low moisture absorptivity, low birefringence and moldability.
However, it involves problems, when used for phase-difference films with an acrylic, pressure-sensitive adhesive agent or the like used for bonding it to a polarizing plate or glass board for liquid-crystal cell, e.g., difficulty for the adhesive agent or the like to exhibit adhesive strength. Similar problems may occur when it is used for a polarizing plate protective film, e.g., insufficient adhesiveness between a polyvinyl alcohol polarizer of very high polarity and norbornene-based polymer of low polarity. Another problem which may be encountered when the polymer of very low moisture permeability is used for a polarizing plate protective film comes from controlled evaporation of moisture in the polarizer to deteriorate optical properties of the polarizing plate during the heat resistance test.
An optical film of thermoplastic norbornene-based polymer has been produced by solution casting, which is unsuitable for mass production because it needs complicated process management which may deteriorate its productivity. Therefore, melt molding processes of higher productivity, e.g., injection molding and extrusion, have been attempted to replace solution casting.
However, melt molding of a norbornene-based polymer, when adopted to produce films, may cause problems, e.g., deteriorated film properties and defective outer appearances caused by decomposition products of the polymer and formation of gel, because the film is exposed to high molding temperature of 250° C. or higher.
Attempts have been made to solve these disadvantages involved in melt molding, e.g., incorporation of norbornene-based polymer with another component, and-modification of the polymer itself.
As one of the former approaches, Japanese Patent Laid-open Publication No.9-221577 proposes a resin composition comprising a thermoplastic norbornene-based resin having a polar group and specific hydrocarbon-based resin. This resin composition, however, involves problems. For example, the molded article of the composition may not have satisfactory optical properties (e.g., haze). Another problem, which may be detrimental, is inapplicability to a thermoplastic norbornene-based resin having poor moisture permeability or the like and containing no polar group. One approach incorporates a thermoplastic norbornene-based resin with a small quantity of polar monomer. However, use of such a monomer is not preferable, because it may cause problems related to compatibility with the resin and its bleeding.
On the other hand, one of the latter approaches decreases molecular weight of a thermoplastic norbornene-based polymer as the starting material. Decreasing the molecular weight, however, may cause a problem of significantly decreased strength of the optical film made of such a polymer.
Under these situations, there are demands for development of novel thermoplastic norbornene-based resin compositions which can be produced by a technique applicable to any type of thermoplastic norbornene-based polymer, whether its base polymer has a polar group or not.
Considering the problems involved in the conventional techniques, it is an object of the present invention to provide a thermoplastic norbornene-based resin composition having improved moldability, moisture permeability and adhesiveness, among others and controlled in thermal degradation and defect formation during the melt molding process while retaining the inherent advantages of norbornene-based resin, e.g., heat resistance and transparency. It is another object of the present invention to provide an article or optical film produced by melt-molding the same composition.